中文摘要：

完美同时签名技术是为解决公平交换问题而提出的，但目前几乎所有的公平交换协议都不提供机密性保护或采用的是先签名后加密的方法，而机密性是公平交换协议极为重要的安全需求。针对该问题，结合完美同时签名与签密技术提出了完美同时签密的概念，并提出了无证书的完美同时签密方案以及在随机预言模型下证明了方案的安全性。另外，该方案对交换双方模糊签密数据的产生顺序没有要求。与“先签名后加密”的方案比较，其具有更短的消息长度以及更少的计算开销，使得方案具有广泛的应用前景。

英文摘要：

Perfect concurrent signature was introduced as an efficient approach to solving the problem of fair exchange of sig- natures. Almost all fair exchange e-commerce protocols that have been proposed until now either do not provide message priva- cy protection or adopt the sign-then-encrypt scheme to provide confidentiality. However, confidentiality is an important re- quirement of e-commerce protocols. This paper proposed a new concept called perfect concurrent signcryption which combined the concepts of perfect concurrent signature and signcryption together to resolve the confidentiality problem in e-commerce sys- tems. It also proposed a certificateless perfect concurrent sigucryption scheme and proved its security in the random oracle model. The scheme published the two ambiguous signcryptions in any order. Compared with the sigu-then-encrypt scheme, this scheme enjoys shorter message length and less operation cost, which makes the scheme has wide application prospects.